a) Field of the Invention
The present invention relates to a refrigerator, and more particularly to a refrigerator for cooling a detector by using electricity and a detecting system using the refrigerator.
b) Description of the Related Art
A semiconductor radiation detecting system detects radiation while cooling a semiconductor radiation detector. This system is widely used not only for measuring radiation such as gamma rays and X-rays at nuclear reactor facilities but also in other radiation measurement fields such as nuclear physics, astro-physics, and nuclear chemistry.
FIG. 17 shows a semiconductor radiation detecting system of a liquid nitrogen cooling type heretofore used. Liquid nitrogen 103 is filled in a double-walled cooling vessel 102. A cooling rod 104 extends from the inner side wall of the cooling vessel 102 through a pipe 108 and the flange 107 mounted on the outer side wall of the vessel 102. A semiconductor radiation detector 101 is mounted on the front end of the cooling rod 104. A vacuum vessel 105 is hermetically mounted on the flange 107. The cooling rod 104 and semiconductor radiation detector 101 are hermetically housed in the vacuum vessel 105. The semiconductor radiation detector 101 is cooled with the cooling rod 104 to a temperature near a liquid nitrogen temperature.
A preamplifier 106 is placed on the side wall of the pipe 108. A radiation detection signal outputted from the semiconductor radiation detector 101 is supplied via lead wires (not shown) to the preamplifier 106 which amplifies the inputted radiation detection signal and supplies it to a radiation signal processing (acquisition) circuit of the rear stage.
FIG. 18 shows a semiconductor radiation detecting system with closed cycle refrigeration system using an He refrigerator, heretofore used. A compressor 110 is coupled to an isothermal compression part 112 by pipes 111. A cylinder 116 extends from the isothermal compression part 112 into a pipe 113. Mounted on a cooling part 114 at the front end of the cylinder 116 is a buffer 115 to which a semiconductor radiation detector 101 is attached.
A vacuum vessel 105 is coupled to the pipe 113. The semiconductor radiation detector 101, buffer 115, and cylinder 116 are hermetically housed in the vacuum vessel 105. Compressed helium adiabatically expands in the cooling part 114 and cools the cooling part 114 which, in turn, cools the semiconductor radiation detector 101 via the buffer 115.
A preamplifier 106 is placed on the side wall of the pipe 113. Similar to the system shown in FIG. 17, the preamplifier 106 amplifiers a radiation detection signal and it to a radiation detection signal processing (acquisition) circuit of the rear stage.
The semiconductor radiation detecting system of a liquid nitrogen cooling type shown in FIG. 17 uses liquid nitrogen to cool the semiconductor radiation detector. It is necessary for the measurement to prepare liquid nitrogen, it is not easy to use the system, and the installation place is restricted. Since the cooling vessel is used, it is difficult to make the system compact.
The closed cycle He refrigerator shown in FIG. 18 inevitably generates vibrations at the cooling part 114 because of its mechanical structures. Vibrations at the cooling part 114 generates microphonic noises. Microphonic noises deteriorate an energy resolution which is an important performance of the radiation detecting system.
The frequency of microphonic noises covers the frequency range near radiation detection signals. It is therefore difficult to eliminate microphonic noises by using only signal processing techniques. In order to reduce the influence of microphonic noises, the buffer 115 is interposed between the cooling part 114 and semiconductor radiation detector 101 for absorbing vibrations. The buffer 115 is required to be cooled during the measurement, and a large cooling ability is necessary.